1. Field of the Invention
This invention relates to an improved method for injecting a two phase fluid through an injection well into subterranean formation.
2. Description of the Prior Art
The injection of a two phase fluid as a step in methods for the recovery of valuable substances from subsurface earth formations has seen increasingly wide use in recent years. Such fluids are perhaps most commonly utilized in the course of recovery processes involving the extraction of hydrocarbons from subterranean reservoirs. Probably the most widely used and most successful of these processes is steam injection wherein the injected steam contains both liquid and vapor water phases. Other commonly used two phase injection fluids useful in petroleum recovery operations are hydrocarbon gas and water mixtures, carbon dioxide and water mixtures, and air and water mixtures to name a few. Steam flooding, carbon dioxide flooding, in situ combustion, and repressurization are all techniques that commonly will employ the injection of a two phase fluid into a subterranean reservoir in order to recover additional quantities of petroleum therefrom. The injection of a two phase fluid is not a process limited solely to petroleum recovery operations, however. It can be utilized in the course of oil shale in situ retort operations, as well as in the leaching of mineral values from subsurface earth formations such as in uranium leaching processes.
Regardless of the specific gas and liquid phases employed or the particular process used, the injection of a two phase fluid is hot without problems, the chief of which is the tendency of the less dense vapor phase to rise to the upper portion of a given vertical injection interval. Another problem concerns the tendency of the gas bubbles to coalesce into larger bubbles which tend to disrupt the entry of uniform proportions of each phase into the formation at any given point along the injection interval. The vertical segregation of the gas phase becomes a problem whenever the bubble rise velocity exceeds the velocity of the fluid as a whole as it is injected downward into the injection interval. One solution has been to inject the fluid at such a rate that the downward velocity of the fluid will always exceed the bubble rise velocity over the entire length of the injection interval. This, however, becomes impracticable and often impossible for injection intervals longer than a few feet in depth. Another solution has been to separate the two phases, injecting the gas phase at the bottom of the injection interval and the liquid phase at the top of the interval. By this method a majority of the gas phase can be induced to enter the lower portion of the injection interval, while the liquid phase enters predominantely into the upper portion of the interval. However, this method requires separate metering and injecting systems for both phases with the associated need for a higher level of supervision and greater expense.
It can be readily seen that there remains a substantial need for a method which provides for the uniform injection of a two phase fluid over an injection interval in a subsurface earth formation.